Online Seminar by Philip Hoehn

Speaker: Philip Hoehn

Place: 241 Nicholson

Date: 14.03.198

Time: 10:30 AM

Title:  From quantum reference systems to quantum general covariance

Abstract: Reference frames (or, more generally, systems) provide the vantage points from which to describe the remaining physics. Treating them fundamentally as quantum systems is inevitable in quantum gravity, where coordinates are a priori unavailable, but also in quantum foundations once accepting that all frames are physical systems. Both fields thus face the question of how to describe physics from the perspective of quantum reference systems and how the descriptions relative to different such choices are related. I will summarize a recent systematic method for such switches, which works in analogy to coordinate changes on a manifold, except that these `quantum coordinate changes' proceed between different Hilbert spaces. This method relies on a new quantum reduction procedure, relating Dirac and reduced quantization, sets the stage for a quantum version of general covariance and applies to both temporal and spatial reference systems. In particular, I will illustrate how one can use this method to switch between different relational clocks in the quantum theory and thereby address the so-called "multiple choice problem of time". (Based on arXiv:1809.00556, 1809.05093, 1810.04153, 1811.00611.)

Online Seminar by Eugenio Bianchi

 

Speaker: Eugenio Bianchi

Place: 241 Nicholson

Date: Thursday Feburary 7th

 Time: 1:30 PM

Title: Entanglement entropy of Bell-network states in LQG

Speaker: Scott Baldridge, LSU
Place: 241 Nicholson
Date: Thursday November 29th
Time: 11am

Title: Graphs and cohomology invariants

Talk by Javier Olmedo

Speaker: Javier Olmedo, LSU
Place: 241 Nicholson
Date: Thursday November 15th
Time: 11am

Title: Power spectrum of primordial perturbations for an emergent universe in quantum reduced loop gravity

Seminar by 

Jonathan Engle

"Deriving loop quantum cosmology from diffeomorphism invariance" 

Loop quantum gravity is an approach to the quantization of general relativity in which Einstein’s principle of diffeomorphism covariance plays a central role. Loop quantum cosmology is a theory in which the principles of loop quantum gravity are applied in the homogeneous, and optionally isotropic, context, leading to predictions for the cosmic microwave background which are the best chance for testing, through observation, the principles of loop quantum gravity. Several results over the years, including a few results by the speaker and collaborators over the last year, have demonstrated (1.) how the Hilbert space of states of loop quantum cosmology and action of basic operators thereon is uniquely determined by the requirement of diffeomorphism covariance, and (2.) the degree to which the dynamics of loop quantum cosmology is similarly determined. This talk will summarize these results.

Skype Seminar by 

Klaus Liegner

"Hamiltonian Renormalisation"
 

We study the question whether it is possible to reformulate the Wilsonian renormalisation group non-perturbatively directly at the operator (Hamiltonian) level. Hamiltonian renormalisation would be the natural route to follow if one had easier access to an interacting Hamiltonian operator rather than to a path integral, at least in the presence of UV and/or IR cut-off, which is generically the case in complicated gauge theories such as General Relativity. Our guiding principle for the definition of the direct Hamiltonian renormalisation group is that it results in the same continuum theory as the covariant (path integral) renormalisation group. We will investigate this direct Hamiltonian Renormalisation for the case of the free massive quantum scalar field and point out its necessity in a concrete cosmological example for Quantum Gravity.

 

Date: Dec 11, 2017

Time: 9 AM

255 Nicholson

Visit by Andrzej Krolak

 

Prof. Krolak  from Institute of Mathematics, Polish Academy of Sciences at Warsaw is visiting us from Nov 27-Dec 6, 2017. Prof. Krolak has made very seminal contributions to our understanding of strength of singularities, and various aspects of theoretical gravity and gravitational waves. He is the head of the Polish gravitatioanal wave community involved with Virgo gravitational wave detector.

You are welcome to discuss with Andrzej in room 255.